Did Apple stop bundling a microfiber cloth in the box? (I guess they did).
Use a microfiber cloth, but be wary of the type that has a pile, especially if they're cheap, or unknown quality. They can scratch (unfortunately, BTDT).
The type that Apple used to include, which have no loops, and are like silk, are better. They're thin, and often have serrated cut edges, not banding, which can also be a source of scratches. The problem with the type that have a pile is that the loops may be soft, but the substrate they're sewn to may not be. Press too hard, and it can scratch.
Be gentle, regardless.